45.4% of consumers report opening and reading an email from a retail brand because the subject link mentioned a discount or special offer. 35.7% said the subject line promoted a product they were interested in. - BlueHornet "2013 Consumer Views of Email Marketing" (2013)

Symbols in subject lines can provide up to a 15 percent lift in open rates - Experian "Email Market Study: Email acquisition and engagement tactics" (2012)

With subject line personalization added in, rates dropped to 5.2%, and 3.2% if the main message was also personalized. Subject line personalization is typically associated with spam, causing most recipients to delete the message or file spam complaints. - MailerMailer "Email Marketing Metrics Report" (2012)

A subject line variation study proved that using the word "free" significantly reduced the amount of click through rates compared to that of a different subject line (17% decrease using the word "free"). - HubSpot "Does the Word 'Free' Affect Email Deliverability & Click-Through Rates?" (2012)

Usage of the words "You" or "Your" appeared in 20.9% of email subject lines from marketers in 2009, compared to 17.2% in 2008. -Experian Marketing Services "The 2010 Digital Marketer: Benchmark and Trend Report" (2010)

Emails that had only the subject line personalized (12.4% Open Rate & 1.7% CTR) did worse than those with no personalization at all (13.5% Open Rate & 2.7% CTR). - MailerMailer (2008)

Seven in 10 US Internet users said they judged these "from" and "subject" lines when deciding whether to report an email as spam. - E-Mail Sender and Provider Coalition and Ipsos (December 2007)

35 percent of email users open messages because of what's contained in the subject line. - Jupiter Research (2007)

Including the company name in the subject line can increase open rates by up to 32 percent to 60 percent over a subject line without branding. - Jupiter Research (2007)

Words that were identified as innocuous words that won't trigger a spam filter, but will negatively affect your open rates. They are: Help, Percent off, and Reminder.- MailChimp (2007)

Personalization such as including a recipient's first name or last name does not significantly improve open rates. - MailChimp (2007)

Providing localization, such as including a city name, does help improve open rates. - MailChimp (2007)

Repeating the exact same subject line for each newsletter accelerates the drop in open rates. While it is important to establish continuity and branding of the newsletter, ideally each new campaign should provide a clear indication in the subject line of what is inside this newsletter that is of interest. - MailChimp (2007)

The general rule of thumb in email marketing is to keep your subject line to 50 characters or less. Our analysis found this to generally be the rule. The exception was for highly targeted audiences where the reader apparently appreciated the additional information in the subject line. - MailChimp (2007)

As a best practice the From and Subject line should work in tandem. The From line should communicate who you are as the sender. As much as possible this entry should not change and should concisely convey who you are. - MailChimp (2007)

Within the category of promotional emails, the same basic rules apply. Keep the message straightforward and avoid using splashy promotional phrases, CAPS, or exclamation marks in your subject lines. Subject lines framed as questions can often perform better. - MailChimp (2007)

An examination of nearly 2,000 subject lines from emails from 94 major online retailers that were sent during February, March and April found that 72% of them were promotional in nature. - Email Experience Council/RetailEmail.Blogspot, "Retail Email Subject Line Study" (June 2007)

Approximately 9% of emails in the sample used hybrid subject lines, those that contain both promotional and non-promotional elements. - Email Experience Council/RetailEmail.Blogspot, "Retail Email Subject Line Study" (June 2007)

More than 39% of the retailers in the study had used at least one hybrid subject line during the 3-month period. - Email Experience Council/RetailEmail.Blogspot, "Retail Email Subject Line Study" (June 2007)

Non-ASCII, non-encoded subject lines broke/rendered incorrectly in both the List View and Message View at 44% of the top tier ISPs, notably AOL, Cablevision, and Earthlink. - Pivotal Veracity (2007)

During the week leading up to Christmas, plus Christmas Day itself, 24% of the emails sent by the largest online retailers promoted e-gift cards, and 27% of those emails mentioned e-gift cards in their subject line. Of all the major e-retailers that sent emails during this period, 29% promoted their e-gift cards in their emails. - Email Experience Council/RetailEmail.Blogspot (January 2007)

69% said they make the decision to click on the "report spam" or "junk" button using the subject line, according to the ESPC. - Email Sender and Provider Coalition (2007)